Here is the source code.
voxel.zip contains the 65c02 assembly source code with the necessary data files (tables, heightmap). You can assemble it using the cc65 tools. There is a .bat file for Windows users to assemble the thing.
simpleVoxel.zip is the tables generator. It computes the tables and displays a test render. You can't move around. This is a VS2017 C++ solution. It relies on the OneLoneCoder Pixel Game Engine to display the render. This game engine fits in a single header file. If you want to easily make games on a modern machine in C++ you should check it out!
voxel.zip
simpleVoxel.zip